Approximately 350,000 deaths occur each year in the United States alone due to Sudden Cardiac Arrest (SCA). Worldwide deaths due to Sudden Cardiac Arrest (SCA) are believed to be at least twice that of the United States. Many of these deaths can be prevented if effective defibrillation is administered within 3-5 minutes of the onset of SCA.
Sudden Cardiac Arrest (SCA) is the onset of an abnormal heart rhythm, lack of pulse and absence of breath, leading to a loss of consciousness. If a pulse is not restored within a few minutes, death occurs. Most often, SCA is due to Ventricular Fibrillation (VF), which is a chaotic heart rhythm that causes an uncoordinated quivering of the heart muscle. The lack of coordinated heart muscle contractions results in a lack of blood flow to the brain and other organs. Unless this chaotic heart rhythm is quickly terminated, thereby allowing the heart to restore its own normal rhythm, death ensues.
Rapid detection, CPR and defibrillation are the only known means to restore a normal heart rhythm and prevent death after SCA due to Ventricular Fibrillation (VF). For each minute that passes after the onset of SCA, mortality typically increases by 10%. At 7-10 minutes, the survival rate is generally below 10%. However, if a patient is effectively defibrillated within 1-2 minutes of the onset of SCA, survival rates can be as high as 90% or more. Therefore, the only known way to increase the chance of survival for an SCA victim is through early detection, CPR and defibrillation.
Rescuers require AED training (also CPR and first aid) by the Red Cross, AHA or other organization on what do during the time when someone has a heart attack until help arrives. The steps that rescuers are trained to perform are:                1. Call'for help. Dial 911 (in the USA) or have someone else do it for you.        2. Assess the victim's condition:                    a) Move the victim's arm and ask or yell “are you okay?”            b) Check to see if the person is breathing                        3. Call for an AED. Most public places have an AED. Ask someone to locate the nearest AED available.        4. Begin CPR. The American Heart Association has recently changed guidelines to encourage lay rescuers (or even bystanders) to perform CPR compressions.        5. Use an AED if available.        
Until recently, first-aid classes taught would-be rescuers to check for a pulse at step (2b) before starting CPR. The AHA now discourages checking for a pulse in an unconscious victim. This is largely because the AHA has found that poorly trained rescuers come to an incorrect conclusion when checking for a pulse in about 35% of cases.
AEDs can easily be found in most public and private places such as schools, golf courses, casinos, restaurants, amusement parks, etc. and have been mandated on airplanes in the USA. As the number of AEDs placed in use increases, so does access to these devices.